Field of the Invention
The present invention relates to an image forming apparatus and a lubricant discharge control method.
Description of the Related Art
In general, an image forming apparatus (a printer, copying machine, or fax machine) which uses an electrophotographic process technology forms an electrostatic latent image by irradiating (exposing) a charged photosensitive drum (image carrier) with laser light based on image data. In addition, the electrostatic latent image is visualized by supplying toner to the photosensitive drum, on which the electrostatic latent image is formed, from a developing device such that a toner image is formed. Moreover, the toner image is directly or indirectly transferred onto a sheet and is thereafter heated and pressed by a fixing nip so as to be fixed, thereby forming the toner image on the sheet.
However, with the demand of image forming apparatuses in recent years for higher resolution, as toner used for image formation, toner having a small diameter and a spherical shape is employed. In a case where the toner having a small diameter and a spherical shape is used, transfer residual toner is likely to slip between a cleaning blade, which scrapes off the transfer residual toner adhered onto the photosensitive drum, and the photosensitive drum.
The reason for this is that, in a case of toner having a small diameter, the force of adhesion between the toner and the photosensitive drum is strengthened by van der Waals forces and thus the toner easily enters a contact portion between the photosensitive drum and the cleaning blade. In addition, in a case of toner having a spherical shape, the toner is likely to slip between the photosensitive drum and the cleaning blade and easily enters the contact portion between the photosensitive drum and the cleaning blade.
In order to solve the problem with the toner on the photosensitive drum slipping through the cleaning blade, for example, JP 2010-230931 A discloses a technique for reducing the coefficient of friction on a photosensitive drum by supplying a lubricant onto the photosensitive drum. In this technique, by supplying the lubricant to the photosensitive drum, the force of adhesion of the toner to the photosensitive drum and the frictional force thereof decrease, and toner can be sufficiently removed by a cleaning blade. In addition, as the toner is easily removed from the photosensitive drum, the force of the cleaning blade contacting the photosensitive drum can be reduced, and an increase in the service life of the cleaning blade and the photosensitive drum can be achieved. Furthermore, due to a reduction in the coefficient of friction of the photosensitive drum, the efficiency in transferring a toner image is improved, and filming caused by foreign matter adhered onto the photosensitive drum and the like can be prevented.
However, when the lubricant supplied onto the photosensitive drum passes through a developing roller part of a developing device, there may be cases where the lubricant is scraped off by a magnetic brush constituted by a carrier and the toner formed on the developing roller and is incorporated into the developing device. When the lubricant is incorporated into the developing device, the lubricant adheres to the toner and thus impedes triboelectric charging between the toner and the carrier. Accordingly, a state in which toner with a reduced charge amount is present in the developing device or a state in which toners which are positively charged and negatively charged coexist with each other is caused. Therefore, there is a problem that image defects caused by fogging, toner scattering, and the like are likely to be generated. Even if the amount of the lubricant supplied to the photosensitive drum is reduced, the lubricant incorporated into the developing device during image formation is accumulated, and it is difficult to solve the problems of fogging and toner scattering through durability.